What is the opening of The Book of Songs? Why use this song and that song?

It's Guanju. I want to use it. The first article shows that the ancestors of China attached great importance to marriage and even family. Because in the eyes of China people, marriage and family between men and women is the foundation and beginning of a society. Guan Ju expressed people's wishes for a beautiful marriage and a happy family. Therefore, in the first chapter of the poem Guanju, "Guanju dove is in Hezhou. My fair lady, a gentleman is a good gentleman ",these four sentences have become people's compliments on the happiness of marriage and family when congratulating the couple, which are often heard in our lives." "